It really depends on what you want to do; personally I wouldn't like eating the same thing day after day so I like to add variety
I use Tripett canned tripe as a topper and also warm water to make it slightly soupy, even my super picky poodle never turns her nose up at it and she's gone over 3 days without eating before.
I wouldn't do actual gravy as most is very high sodium. Rather, use things like canned dog food, Greek yogurt, hamburger (either raw or cooked), chicken (either raw or cooked), just for a few ideas. I wouldn't use a lot, after all you want them eating mostly kibble but just enough to make it irresistible for the dog
Jasmine - Female Miniature Poodle - born Aug 15, 2010
Loker Delgado Von Stalworth - Male GSD - born Jan 26, 2012
Koda & Zazu - 5 year old male cats
Alex - Male Cocker Spaniel (rescue) - RIP Cuddlebug 2007-2010